Issue:
======
Remote Procedure Call (RPC) is a protocol used by the Windows
operating system. RPC provides an inter-process communication
mechanism that allows a program running on one computer to
seamlessly execute code on a remote system. The protocol itself
is derived from the OSF (Open Software Foundation) RPC protocol,
but with the addition of some Microsoft specific extensions.

There is a vulnerability in the part of RPC that deals with
message exchange over TCP/IP. The failure results because of
incorrect handling of malformed messages. This particular
vulnerabilty affects the RPC Endpoint Mapper process, which
listens on TCP/IP port 135. The RPC endpoint mapper allows RPC
clients to determine the port number currently assigned to a
particular RPC service.

To exploit this vulnerability, an attacker would need to
establish a TCP/IP connection to the Endpoint Mapper process on
a remote machine. Once the connection was established, the
attacker would begin the RPC connection negotiation before
transmitting a malformed message. At this point, the process on
the remote machine would fail. The RPC Endpoint Mapper process
is responsible for maintaining the connection information for
all of the processes on that machine using RPC. Because the
Endpoint Mapper runs within the RPC service itself, exploiting
this vulnerability would cause the RPC service to fail, with the
attendant loss of any RPC-based services the server offers, as
well as potential loss of some COM functions.

Microsoft has provided patches with this bulletin to correct
this vulnerability for Windows 2000 and Windows XP. Although
Windows NT 4.0 is affected by this vulnerability, Microsoft is
unable to provide a patch for this vulnerability for Windows NT
4.0. The architectural limitations of Windows NT 4.0 do not
support the changes that would be required to remove this
vulnerability. Windows NT 4.0 users are strongly encouraged to
employ the workaround discussed in the FAQ in the bulletin,
which is to protect the NT 4.0 system with a firewall that
blocks Port 135.

Mitigating Factors:
====================

- - To exploit this vulnerability, the attacker would require the
ability to connect to the Endpoint Mapper running on the target
machine. For intranet environments, the Endpoint Mapper would
normally be accessible, but for Internet connected machines, the
port used by the Endpoint Mapper would normally be blocked by a
firewall. In the case where this port is not blocked, or in an
intranet configuration, the attacker would not require any
additional privileges.
- - Best practices recommend blocking all TCP/IP ports that are not
actually being used. For this reason, most machines attached to
the Internet should have port 135 blocked. RPC over TCP is not
intended to be used in hostile environments such as the internet.
- - More robust protocols such as RPC over HTTP are provided for
hostile environments. To learn more about securing RPC for
client and server please refer to
http://msdn.microsoft.com/library/default.asp?url=/library/en- us/rpc/rpc/writing_a_secure_rpc_client_or_server.asp. To learn
more about the ports used by RPC, please refer to
http://www.microsoft.com/technet/prodtechnol/windows2000serv/res kit/tcpip/part4/tcpappc.asp
- - This vulnerability only permits a denial of service attack and
does not provide an attacker with the ability to

Risk Rating:
============
Important

Patch Availability:
===================
A patch is available to fix this vulnerability. Please read the
Security Bulletins at

Acknowledgment:
===============
- Microsoft thanks jussi jaakonaho for reporting this issue to
us and working with us to protect customers

- ----------------------------------------------------------------

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